Characterisation and bioactivity of an exopolysaccharide isolated from Lactobacillus rhamnosus LRH30 cultivations

This study presents the first characterisation of the exopolysaccharide (EPS) produced by Lactobacillus rhamnosus LRH30 (L. rhamnosus LRH30) in skim milk-based bioprocesses. EPS yields varied significantly with cultivation mode, reaching 200.8 mg/L in shake flask, 427 mg/L in batch, and 1866 mg/L in fed-batch fermentation. When dissolved in milk, the EPS exhibited shear-thinning behaviour, indicating its suitability for texture enhancement in dairy applications. Morphological analysis via scanning electron microscopy (SEM) revealed a flaky, spherical microstructure. Fourier-transform infrared spectroscopy (FTIR) showed characteristic polysaccharide peaks, with similarities to commercial dextran. Monosaccharide composition analysis by high-performance liquid chromatography (HPLC) identified glucose and rhamnose as the dominant constituents. Bioactivity assays demonstrated dose-dependent immunomodulatory effects: EPS at 50 µg/mL significantly increased IL-10 and decreased TNF-α in LPS-stimulated macrophages. Additionally, IL-6 was reduced at 5 µg/mL, while IL-1β increased at 50 µg/mL. The EPS also exhibited moderate antioxidant activity, with a maximum radical scavenging capacity of 39.2 %. These findings highlight the potential of the EPS from L. rhamnosus LRH30 EPS as a novel, multifunctional ingredient for use in dairy-based functional foods.